Scout had already gotten closer to the Radley house than she had ever planned when the tire in which she was riding rolled onto the Radley's front steps. When her head finally cleared, she realized that she was staring right at the steps that led the dreaded Radley porch. She ran as fast as she could back to Jem and Dill, and Jem questioned her about why she didn't retrieve the tire, which was now in the Radley yard. Jem summoned the courage to bring it back himself. Scout does not mention it at the time, but following Atticus' admonition to stop playing their game, she decided that this was a second good reason to stop. She had heard laughter coming from inside the Radley house while she was on the step, and she must have realized that it was probably coming from Boo.